Most non-hybrid vehicles include an internal combustion engine coupled to a transmission and a final drive to rotate wheels that move the vehicle. To start the engine of a non-hybrid vehicle, a starter motor is energized, which causes a crankshaft of the engine to turn and start the engine.
Many hybrid electric vehicles utilize both an electric motor-generator and an internal combustion engine to offer reduced fuel consumption and emissions. One type of hybrid electric vehicle utilizes a belted-alternator-starter (BAS). The BAS utilizes a motor-generator coupled to a crankshaft of the engine, usually by a belt and pulley system. The motor-generator can draw power from an energy storage device to generate torque that is used to rotate the engine when a brake is released at a stop light, in order to start the engine, or to supplement engine drive torque that is used to propel the vehicle. When torque from the electric motor-generator is used to supplement torque from the engine for vehicle propulsion, the hybrid vehicle is often referred to as operating in a “boost” operating mode. The electric motor-generator may also be rotated by the engine to generate electricity that is used to recharge the energy storage device. When the electric motor-generator is powered by the engine to generate electricity for charging the energy storage device, the hybrid vehicle is often referred to as operating in a “regenerative” operating mode. A hybrid system controller controls the operation of the electric motor-generator to operate the electric motor-generator in either the boost operating mode or the regenerative operating mode.